1. Field of the Invention
The present invention relates to a novel iron-containing aluminosilicate. More particularly, it relates to a novel aluminosilicate containing iron or an iron compound in its high activity condition, a process for efficiently producing the iron-containing aluminosilicate, and a process for hydrocracking heavy oil by the use of a catalyst containing the iron-containing aluminosilicate.
2. Description of the Related Arts
Aluminosilicates containing iron have heretofore been used as a catalyst for various reactions such as hydrocracking of heavy oil and disproportionation of toluene (e.g., Japanese Patent Application Laid-Open Nos. 2214/1983, 34891/1983, 47088/1983, 103588/1983 and 138788/1983).
It is known that in the preparation of an iron-containing aluminosilicate as described above, a Y-type zeolite subjected to a steaming treatment as well as a Y-type zeolite is used as the starting material of the aluminosilicate. It is reported that in the hydrocracking of heavy oil, the Y-type zeolite subjected to a steaming treatment provides higher selectivity for yield of middle distillate than the Y-type zeolite does (e.g., Japanese Patent Application Laid-Open Nos. 103588/1983, 92026/1984, and 64914/1988).
However, an iron-containing steam treated aluminosilicate as described above is unsatisfactory in hydrocracking activity and, moreover, iron is not uniformly contained or deposited. Thus the aluminosilicate is not satisfactory in its practical use in respect of stability and activity.
One of the problems using a steam treated aluminosilicate as the starting material is that aluminum constituting the crystal skeleton partially drops off, consequently covering the surface of the crystal. An iron molecule in an iron salt solution takes various states depending on pH, temperature, concentration, coexisting elements, and so forth of the solution. Some active iron molecules for various reactions, therefore, tend to irreversibly change into an inactive state with a slight change in circumstances. It is believed that if an iron salt reacts with aluminum on the surface, inactive iron is liable to be deposited. Thus it is very difficult to obtain an aluminosilicate containing iron in its high activity form in a stabilized manner.
In order to overcome the above problems, it was attempted to improve the state of iron contained or deposited by washing the surface through treatment with mineral acid after steaming. From this viewpoint, a method of preparing iron-containing aluminosilicate, comprising a combination of mineral acid treatment and iron salt treatment has been developed (Japanese Patent Application Laid-Open No. 121115/1984). In accordance with this preparation method, filtration, washing and calcination are conducted after treatment with mineral acid and, thereafter, an iron salt treatment is applied. It has been found, however, that if filtration, washing and calcination are carried out after treatment with mineral acid, modification of the aluminosilicate surface occurs, leading to a change in the deposition state of iron and at the same time, the amount of iron deposited becomes unsatisfactorily low.